Hydraulic brake apparatus for



Jan. 22, 1935. E, G. CARROLL Re- '19,432

HYDRAULIC BRAKE APPARATUS FOR AUTOMOBILES Original Filed Aug. 20, 1927 2Sheets-Sheet. l l

I' VA." I je l J \2 2827 gfx/vanto@ 19e/fe GT Carro/ 2%@ Jan. 22, 1935.E. G. CARROLL Re 19,432

HYDRAULIC BRAKE APPARATUS FOR AUTOMOBILES Original Filed Aug. 20. 192'?2 Sheets-Sheet 2 Carro/A Reissued Jan. 22, 1935 HYDRAULIC BRAKEAPPARATUS FCB. AUTOMGBILES Eugene G. Carroll, Los

Angeles, Calif., assignor,

by mesne assignments, to Bendix Brake Company, South Bend, Ind., acorporation of Illinois- Original No. 1,770,064, dated July 8, 1930,Serial No. 214,330, August 20, 1927. Application for reissue July 7,1932, Serial No. 621,295

40 Claims.

This invention relates to a uid actuated, or hydraulic brake apparatusand is intended especially for use on automobiles. Such an apparatususually includes a master cylinder in which a piston moves. When thispiston is operated by the brake pedal, the pressure of the iluid orliquid in front of the piston is raised and imparted to the hydraulicbrake cylinders at the wheels. Theoperating liquid is supplied to the minterior of the-master cylinder through a port located just in front ofthe position of the piston when the brake is in its inactive position;that is to say, when the brakes are oft, In this type 'of apparatus themaster cylinder has been provided with a head through which a stem, orpiston rod, slides in order to operate the piston, and the cylinder isprovided with a by-pass port which connects the chambers in front of'the piston and back of the piston when the piston is in its inactiveposition. With that arrangement a dilculty has arisen by reason of thefact that when the piston is moved forwardly a quantity of liquid infront of the piston passes through the by-pass port around to thechamber at the rear of the piston and, therefore, there is a loss in thequantity of liquid in front of the piston. This interferes with theeifectlve application of `the brakes. This diiliculty is not overcome bymaintaining the liquid in the cylinder in front o1' the piston underpressure, because, even if pressure does exist, the by-passing occursjust the same, and, consequently, there is the ei'- i'ect of-lost motionin the rst part oi' the movement of the piston. The general object ofthis invention is to overcome this difliculty and to provide a mastercylinder in which the increase in pressure in the cylinder in front ofthe piston will begin immediately when the piston begins its advance forthe braking movement.

In the operation of automobile brakes oi the four-wheel type, it hasbecome recognized as bad practice to have the front wheels braked withgreater force than the rear wheels. In other words. the braking actionshould be greatest on the rear wheels. One of the objects of thisinvention is to provide an apparatus which will automatically insurethat the braking effect on the front wheels will be less than that onthe rear wheem; also to construct the apparatus in such a way that'incase the braking apparatus for the rear wheels. or for the front wheels,should become inactive then the braking apparatus for the other wheelswill continue to function effectively. In other words, according to myinvention, 1 provide a dual systemlfor the rear wheel brake cylindersand for the front wheel brake cylinders, connected up in such a way thatthere is an equalizing pressure connection between the two apparatusespreventing the application of too great power to the front wheels, butenabling the rear wheel braking apparatus to continue toiunctionproperly in case the front wheel braking apparatus gets out oforder, and vice versa.

This is accomplished automatically and without any adjustment orattention being necessary from the driver of the car.

Further objects of the invention will appear hereinafter.

The invention consists in the novel parts and combination of parts to bedescribed hereinafter, all of which contribute to produce an eiiicientfluid brake apparatus for automobiles.

A preferred embodiment of the invention is described in the followingspeciiication, while the broad scope of the invention is pointed out inthe appended claims.

In the drawings: f

Fig. l is a general view diagrammatic in its nature but showing theprincipal parts of the apparatus in cross section and indicating theconnections to the front and rear wheels;

Fig. il` is a plan showing a twin cylinder construction with connectionsto the rear and front,v This view particularly illustrates the. in-

the line 4-4 of Fig. 3; and

Fig. 5 is a longitudinal section through a master cylinder o1' the typeillustrated in Fig. 1 but showing another embodiment of the inventionwhich avoids the necessity of using a pressure reservoir and anauxiliary relief reservoir such as illustrated in Fig. 1. l

Referring to the parts of the apparatus, and particularly to Fig.' .1,in this embodiment of the invention I provide a master cylinder 1. Ishall now describe the'improvements I'employ'in connection with thiscylinder to overcome the objections referred to in the statement of myinvention; namely, the loss of pressure in the master cylinder in frontof the piston, due to the escape of liquid that by-pa es the advancingpiston. As regards this feature of my invention, it should be understoodthat this improvement can Fig. 4 is a horizontal section taken about onvchambers 2 and 3; the former may be considered as the forward chamber ofthe cylinder and the latter the rear chamber. The forward bore 2, at itsforward end, is provided with a pipe con'- nection R. leading to thebrake cylinders at the wheels. This connection R may lead to brakecylinders at the two rear wheels or it may lead to brake cylinders atall four wheels. I provide means for maintaining the pressure in theforward bore as its piston advances across its fluid supply portreferred to hereinafter as port 6. In the bore 2 I provide a plungerhaving a piston 4, preferably of relatively small diameter, and in thebore 3 I provide a piston 5 preferably of rel-A atively large diameter.I provide a by-pass port connection around the piston 4, which allowscommunication between chambers 2 and 3. In

the present instance, this connection includes two passages 6 and 7communicating with a small chamber 8, the port 6 passing through thewall of the cylinder into the bore 2 slightly in advance of the positionof the piston 4 when the brakes areinactive; that is to say, when thebrakes are oil 'Associated with this port connection between the twochambers 2 and 3, I provide a 'check valve 9 which permits the flow fromthe chamber 3 through the connection but 1which prevents `flow throughthe connection from 'the vchamber 2 toward the chamber 3.

connected with the piston 4 through a strut link 12. This is thearrangement which I prefer to employ where the two bores 2 and 3 are intandem with each other in order to facilitate the use of tandem pistons,as illustrated.

Operating' liquid under pressure is supplied to the bore 3 through avalve chamber 13 provided with a valve 14 mounted over a port 15 leadinginto the interior of the bore from the valve chamber 13. The operatingiluid is admitted through a pipe connection 16 mounted in a screw plug17 the latter being formed with an admission port 18 in its lower endcommunicating with the valve chamber 13. With this arrangement it isevident that upon the suddenv increase in pressure in the chamber 3 thevalve 14 would. rise and -come against the lower end of the plugl'lthere-v by closing the outlet through the port 18. e

With the apparatus already described it will be evident that when thepistons 4 and 5 advance in the braking movement, the movement of thepiston immediately causes a differential action or the pistons,involving an increase in pressure in the liquid in the chamber 3,causing a flow of liquid through the port '7 into the chamber 8, andthis produces a press at this point which prevents an escape of liquidthrough the port 6 as the-piston 4 advances, and fact may cause a iiowfroxnthe larger cylinder into the smaller cylinder thus aiding in themovement of liquid from the smaller cylinder toward the brakes.

Where a rise in pressure is produced in the chamber f5,y the excess ofthe liquid under pressure may flow through the plug to a pressurereservoir 19 the bottom of which is connected by pipe connection .20 tothe plug.

As additional means for preventing eillux from port 6 I prefer also toprovide a check valve or its equivalent in the syst-em, insuringimmediate compression of the liquid in advance of piston 4 when itadvances. This valve maybe located at'the reservoir 19 as will nowappear.

The pressure reservoir 19 is at all times completely filled with theoperating liquid. At its upper side it is preferablyv provided with arelief outlet 20a including Va valve 21 held on its seat by a spring 22.this relief valve 21 will be collected in an auxiliary or overflowreservoir 23. Liquid which passes the valve may be returned to thechamber 3 through the pipe 16 which,.in the present instancefisconnected to the relief valve between the pressure reservoir 19 and theoverfloweservoir 23. As illustrated, the pressure reservoir 19 is shownas a dual reservoir. That is its preferred form when used with a dualsystem in which thereis a pressure piston corresponding to the frontwheels and another pressure piston corresponding to the rear wheels. Ishall now proceed t6 describe the features of this master cylinder whenit is adapted to the dual type of brake apparatus'.

When the master cylinder is adapted to the dual type it is provided withan extension 24 -having a bore or chamber 25 of smaller diameter thanthe bore 2. This bore 25 carries a piston 26,' the left end 27 of whichis exposed tc the pressure of the liquid in the chamber 2. When thepiston 4` advances in the braking movement the rise of the pressure inthe chamber 2 causes a movement of the piston 26 toward the right,thereby compressing the liquid in the chamber 25 land communicating thispressure through the connection Fjto the hydraiic cylinders ofv theforward wheels. I prefer to provide a slip connection 28 between thepiston 4 and the'piston 26. This slip connection comprises a threadedshank 29 over which a threaded coupling 30 is screwed. This coupling 30has an opening 3l through it to receive the shank of a pin 32, or bolt,that is threaded into the adjacent end of the piston 26. Between thehead 33 of this connecting bolt and the end of the shank 29 a gap orspace 34 is formed. In the normal operation of the brake apparatus thisgap would not close Any liquid that escapes through because thedevelopment of pressure in the chamf ber 2 by the movement of the piston4 would cause the piston 26 to advance before the end of the shank 29engaged the head 33.` lWith this organization of parts it will beevident that whatever pressure is developed in the chamber' -2 by theladvance of the 'piston 4', a correspondand hence whenever the brakes areapplied thereC I wii be a greater quantity cf liquid forced into theconnection R. than would ce forced.' inta the connection F to the frontwheels. This gives the front wheels a. relatively low braking power,which is to be desired.

The liquid under pressure may be supplied to the chamber 25 through apipe connection 35' leading to it from the pressure reservoir 19.` If

.desired the pressure reservoir 19 can be constructed so that it'has twochambers, 19a and 19h, the former of which is connected to the pipeconnection 20 leading to the bore 2 and the latter of which supplies theliquid to the bore 25.

The liquid for the system may be supplied by removing a plug 36 in thecover of the overow reservoir ,23. The .level of the liquid in thesystem may be at the point indicated by the line 37. It will beunderstood that the overilow tank 23 need not be under pressure and isvented to the atmosphere through the plug 36.

Referring again tothe chambers 2 and 25, it should be understood that inthe operation of the apparatus, the .piston 26 operates as a pressureequalizer between these chambers. This results by reason of the lostmotion connection between the head 33 and the end of the shank 29. Ifthe .pressure is low in chamber 2 there will be more movement at thisconnection and less effective advance by the plunger 26.

I shall now describe an embodiment of an equalizer which in operationequalizes the pressure in the liquid that operates the rear brakes andthe liquid that operates the front brakes. Referring particularly toFigures 2 to'4 inclusive, in this feature of the invention I provide anequalizng cylinder 38 in which there is located a movable piston 39.This movable piston is normally at an extreme point in the cylinder 38,being held there by a coil spring 40. This spring is simply a lightreturn spring and requires only a very light force to compress it. Inthis way two equalizing chambers 4l and 42 are formed, the former ofwhich is connected by a connection F' with the forward brakes while thechamber 42 is connected by a connection R with the rear brake cylinders.

The iluid pressure in the two chambers 41 and 42 will be developed bytheadvance of their-'pistons 43A (see Fig. 3) in the bores or chambers 44,the inner ends of which communicate respectively with the chambers 41and 42 through two passages, such as the branch passage 45 (see Fig. 3).responding pipe connection F' or R. the cylinders 44 may be castintegral with the cylinder 38 which is located on their end as a crosscylinder. The tvo chambers 44 are arranged in tandem with two bores 46of slightly larger diameter, the latter being provided with theircorresponding pistons 47. These pistons 47 may be advanced in unison bystems 48 attached to a cross head 49 operated by strut link 50connecting with the brake pedal. Liquid under'hydro-static pressure issupplied to the chambers 44 and 46 through two passages 51 each of whichmay have two branches 52 corresponding to each of the associated bores.These passages are most conveniently formed in bosses 53 connected bypipe connections 54 with a dual reservoir 55 in which the operatingliquid is carried. The liquid level in this reservoir may be at thepoint indicated by the line 56. The upper part of the reservoir 55operates as an'air chamber 57, air being admitted through a valve 58which opens inwardly and is normally held on its seat by a coil spring59. When the liquid level falls in this reservoir and a partial vacuumis developed in it, this valve will open and admit air through a portEach passage 45 communicates with its cor- If desired i 60 in a plug 61mounted in the upper end of the' valve casing.

Another embodiment of the invention is illustrated in Fig. which avoidsthe necessity of employing. reservoirs for the operating liquid. In thisview 62 represents the master cylinder having two bores 63 and 64, thelatter of which is of slightly larger diameter than the former. Thesebores are connected by a port 65 which by-passes the small piston 66.The chamber or bore 64 is connected through a bore 67 with a smalloverflow chamber 68 which is in the form of a. small cylinder orbosscast into the wall of the cylinder 62 and provided with a piston 69pressed down by a spring 70 which thrusts at its upper end against aremovable screw plug 7l. The piston 66 is .connected by a rod 72 with apiston 73 of large diameter working in the bore 64. With thisorganization of parts when the pistons 73 and 66 are advanced in unisonby a force imparted from the brake pedalthrough the part 74, the rise inpressure in the chamber 64 merely causes a flow through the port 65 intothe chamber 63 thereby preventing a loss of pressure such as might occurby an outward flow of liquid in this port from thechamber 63 as thepiston 66 advances. Therefore, the advance of the piston 66 merelycauses arise in pressure in the chamber 63 which is communicated to thebrake cylinders connected to this cylinder through a connection similarto the connection R.

Any suitable brake cylinders may be employed with the brake apparatusdescribed above. In Fig. 1, I illustrate a common type of brake cylinderincluding a cylindrical casing 75 with a middle chamber 76 to which theliquid under pressure is admitted. The pressure in this liquidv pressesout the lpistons 77 and the movement of lthe pistons is communicatedthrough rockers 78 to the ends of brake band 79. The chamber 3 operatesof course to catch any leakage from the chamber 2 pasty the piston 4.

In the operation of the apparatus shown in Figs. 2 to 4, if the pressurein the chamber 42 should fail or drop, vthe piston 3 9 will be movedover, (which movement will be permitted by the spring), automaticallyenlarging the 'chamber 41 and in this way automatically reducing thepressure in the chamber 41. This automatically -reduces the brakingpowerof the forward brakes.

In this way the pressure for yapplying their braking power will alwaysbe kept as low as that of the rear brakes. But if either side of thesystem should break down the other side will continue to functionproperly.

A disclosure similar to the showing of Figure 3 hereof is `also shownand is claimed in my copending application 270,286. l

Figures 2, 3 and 4 are also shown and the arrangement of the floatingpiston 39 is claimed inmy Patent 1,978,669.

The additional inventive features specically disclosed in the embodimentof Figure 5 are speciflcally claimed in my copending application SerialNo. 270,286.

It is understood that the embodiments of the invention described hereinare not the only embodiments which this invention may take, and

with a'piston working therein, there beings. port leading into said boreimmediately in advance of the piston when in its inactive position, forsupplying operating liquid to the bore, connections from the" bore tothe brake cylinders at the wheels and means for maintaining apredeterminedvpressure in said port broughtinto action while the pistonis advancing, operating to prevent efilux of liquid from the vborethrough the port and thereby preventing loss in the volume of liquid infront of the piston as it advances.

2. In a hydraulic brake apparatus for an automobile having brakecylinders at the wheels-the combination of cylinder means having twobores, pistons workingn said bores in unison with each other, one ofsaid bores being of relatively small diameter and connected with thewheel brake cylinders, and the other bore being unconnected with thebrake cylinders, and of relatively large diameter, said bores having aport connecting the same, the large piston operating in its forwardmovement to prevent loss in the volume of liquid in front of the pistonof smaller diameter as it advances.

'3. In a hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination of a master cylinder having twobores with pistons working in said bores in unison with each other, oneof said bores being ot relatively small diameter and connected with thewheel brake cylinders, and the other of sid'bores being unconnected withthe brake cylinders andv of relatively large diameter, said small borehaving a port for supplying the operating liquid to the same, located inthe wall o! the cylinder in front oi the small piston when in itsinactive position, said port being in communication with the large boreand operating to maintain the pressure ot the operating liquid at saidport and prevent escape o! the operating liquid from the small bore onthe forward stroke oi' the pistons'when the brakes are being applied.

4. In a hydraulic brake apparatus for auto mobiles having brakecylinders at the wheels, the combination of a master cylinder having twobores with pistons working in said bores in unison with each other, oneof said bores being ot relatively small diameter and connected with thewheel brake cylinders, and the other of said bores being of relativelylarge diameter, said small bore having a port for supplying theoperating liquid to the same, located in the wall of the cylinder infront o! the small piston when in its inactive position, said port lingin communication with the largev bore, means for maintaining a supply ofliquid'under pressure in communciation withthe said port,'said pistonscooperating in their forward movement in applying the brakes, to developa movement of liquid from the large bore toward the said port andthereby prevent escape ot liquid through the said port from the smallbore as its piston advanvces. 15. In a hydraulic brake apparatusfcrautomobiles having brake cylinders at the wheels, the

' relatively small diameter and connected with the wheel brakecylinders, andthe other of said bores being of relatively largediameter, said small rbore having a port for supplying the operatingliquid to the same, located in the wall of the "cylinder in front of thesmall piston when in its inactive position, 'a pressine chamber formaintaining a quantity of operating liquid under pressure, avalve-chamber communicating with the same, and with said port, andhaving a. leading from the large bore with a check-valve to permit flowfrom the large bore into the valvechamber, the said pistons operating intheir forward movement in applying the brakes, to develop a movementoiliquid from the large bore into the said valve-chamber and therebysupply liquid under pressure to the said iirst-named port land preventescape oi liquid through the said iirst named port from the small boreas its piston advances. Y

6. In a hydraulic brake apparatus for automobiles having brake cylindersat the wheels, the combination of a master cylinder having two boreswith pistons working in said bores in unison with each other, one ofsaid bores being of relaconnecting the reservoir with the large cylinder-for maintaining the liquid under pressure.

7. In a hydraulic brake apparatus tor automobiles having brake cylindersat the wheels, the combination of a master cylinder having two unisonwith each other, one ot said bores being oi relatively small diameterand connected with the wheel brake cylinders, and theother of said boresbeing ofV relatively large diameter, 'said small bore having a portcommunicating with the large bore for supplying the operating liquid tothe small bore, located in the wall` of the cylinder in front of thesmall piston when inits inactive position, and a valve associated withthe port for, permitting ilow of liquid from the large bore toward thesmall bore Abut operating to check the flow of liquid from the smallbore toward the large bore.

. 8. In av hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the

combination of a master cylinder having two bores with pistons workingin said bores yin unison with each other, one of said bores being ofrelatively small diameter and connected with the wheel brake cylinders,and the other of said bores .bores with pistons working' in said boresin y being o! relatively large diameter, said small' bore having ag portcommunicating with the large bore for supplying the operating liquid tothe small bore, located in the wall of the cylinder in front of thesmall piston when in its inactive position, a valve-chamber in the wallof the cylinder communicating with the said port, av

valve therein operating to permit ow of liquid through-the port from'thelarge bore toward the small bore and to check the flow from the smallbore toward the large bore, and a pressure reservoir communicating withthe valve chamber for supplying the same with liquid under pressure.

v9. In alhydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination of a master' cylinder havingtwo bores with pistons working in said bores in unison witheach other,one of' said boresl being of relatively small diameter and connectedwith the wheel brake cylinders, and. the other of said bores being ofrelatively large diameter, saidv small 'bore having a port for supplyingthe operating liquid to the same, located in the wall of the4 cylinderin front of the small piston when in its inactive position, a pressurereservoir having a connection communicating with the said port, withmeans connected with the larger bore for maintaining liquid underpressure in communication with the port, and a by-pass beyond the pointof connection of the said pressure reservoir for returning liquid to thelarge bore to maintain the same completely full.

10. In a hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination oi. a master cylinder havingtwo bores with pistons working in said bores in unison with each other,one of said bores being of relatively small diameter and connected withthe wheel brake cylinders, and the other of said bores being ofrelatively large diameter, said small bore having a port communicatingwith the large bore for supplying the operating liquid to the smallbore, located in the wall of the cylinder in front of the small pistonwhen in its inactive position, the said pistons operating in theirforward movement in applying the brakes, to develop a movement of liquidfrom the large bore toward the said port and small bore, meansassociated with the port for checking back flow of liquid passing fromthe large bore, and automatic means for replenishing the large bore withliquid to main- Vtain the same completely full.

11. In a hydraulic brake apparatus for automobiles having brake`cylinders at the wheels, the combination of a master-cylinder havingtwo bores arranged in tandem, with tandem pistons working in said boresin unison with each other, one of said bores being of relatively smalldiameter and connected with the wheel brake cylinders, and the otherbore being of relatively large diameter, said cylinder having a portconnecting said bores, means for supplying liquid under pressure to thesmall bore, a connection for supplying liquid to the large bore andincluding a check valve operating to close when the pistons moveforwardly in applying the brakes so that the said pistons co-operate todevelop a iiow of liquid from the large bore through the port to thesmall bore. i

12. In a hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination of a master cylinderhaving amovable piston therein for developing pressure within the cylinder, aconnection from the master cylinder to the cylinders of the wheelbrakes,

, said master cylinder having a forward chamber for the said piston, anda rear chamber back of the piston collecting any liquid leaking into thesame past the' piston, a pressure reservoir for the liquid for supplyingliquid under pressure to the cylinder in front of the piston, saidpressure reservoir having an auxiliary reservoir with a relief outletfrom the pressure reservoir into4 the auxiliary reservoir and aconnection from the auxiliary reservoir for returning liquidthatcylinder to the cylinders of 'the wheel brakes, said mastercylinderhaving a rear chamber back of the piston, a pressure reservoirfor the liquidfor supplying liquid under pressure to the chamber infront of the piston, an auxiliary reservoir with a relief outlet intothe same from the pressure reservoir, and a connection from theauxiliary reservoir for returning liquid that passes the relief outlet,to the rear chamber of the cylinder, said cylinder having a portconnecting the rear chamber of the cylinder with the front chamber witha check valve preventing the ilow of liquid from the front end of thecylinder into the rear for supplying the operating liquid under pressureto the said chamber through said port, and means for vdeveloping anabnormally high pressure in the liquid in said vport when the pistoncommences its forward movement when the brakes are being applied, toprevent loss of liquid through said port from the said chamber.

15. In a hydraulic brake apparatus for automobiles, the combination of amaster cylinder having 4a. forward chamber with a movable piston thereinfor developing pressure in the forward chamber inA front of the piston,said cylinder having a rear chamber of larger diameter than the forwardchamber back of the piston with a port connecting the two chambers,means for supplying the operating liquid under pressure to the saidforward chamber through said port and including a pressure reservoirwith a relief outlet, a return connection beyond the relief outlet forleading liquid back into the rear chamber, with a check-valve, a secondpiston located back of the rear chamber and connected with the rstpiston, said second piston operating when the pistons are movedforwardly to apply the brakes to develop pressure in the rear chamber,operating to close the check valve in the return connection and forceliquid from the rear chamber through the port and thereby preventoutward flow from the forward chamber through said port.

16. In a hydraulic brake apparatus for automobiles having brakecylindersat the wheels, the combination of a master cylinder having two bores ofdifferent diameters, a piston corresponding to each bore and movabletherein, means for supplying operating liquid to the said bores, ,thepiston in the smallerbore being mounted so that the liquid pressuredeveloped in the large bore is imparted to it and operates to advance itn its own bore, a connection from the larger bore to the brake cylindersof the rear wheels and a connection from the smaller bore tol the brakecylinders of the forward wheels.

17. In a hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination of a master cylinder having twobores arranged in tandem, one of said bores being of relatively smalldiameter and the otherbore of relatively large diameter, aA pistonmovable in the large bore and having means for operating the same by apedal to apply the brakes, means for supplying the operating liquid toeach bore in front ofits piston, the relatively small piston beingexposed to the liquid pressure defrom the large bore to the rear brakecylinders and a connection from the smaller bore to the forward brakecylinders.

i3. In a hydraulic brake apparatus for auto- .mobiles having frontwheels-and rear wheels and brare cylinders at the wheels, thecombination of a cylinder with a bore corresponding to the trent wheelsand having a piston and a connection from the bore "the front 'wheelbrake cylinders, a second bore corresponding to the rear wheels with.its en and a connection from it to the rear bre-Tae cylinders, means forconnecting the last named piston with the brake pedal to enable pressureinthe last named bore to be developed to apply the rear brakes, the nrstnamed piston being mounted so that it is exposed to the liquid pressuredeveloped in the second named bore so as to be advanced thereby anddevelop pressure for braking the forward wheels, and a. slip connectionbetween the two pistons. enabling the piston that operates the brakes ofthe rear wheels to positively advance the other pistonY in case there isno pressure developed in the bore corresponding to the rear wheels.

19. In a hydraulic brake apparatus for automobiles having brakecylinders at the wheels, the combination of 'a master cylinder havingtwo bores of diilerent diameters, a piston corresponding to each boreand movable therein, means for supplying operating liquid to the saidbores, the piston in the smaller bore being capable of limited relativemovement with respect to the piston in the larger bore, and mounted sothat the liquid press-ure developed in the larger bore is impartedv toit and exerts pressure on its rear face to advance it in its own bore, aconnection from the' larger bore to the'brake cylinders oi the rearwheels, and a connection from the smaller bore to the brake cylinders ofthe forward wheels.

20. A hydraulic brake apparatus as claimed in claim 19, in which thebores are of different diam-- eters arranged in tandem to each other andhaving a connection between the same` with a lost motion device wherebythe pressure developed in the rear bore is imparted to the rear face ofthe plunger of smaller diameter.

21. In a fluid actuated brake apparatus for an automobile havingfluid-actuated brake cylinders at the wheels, the-combination ofcylinder means having two bores, pistons mounted in said bores, meansfor imparting movement from one piston to the other, means connectingone of said bores with the wheel brake cylinders to apply the brakes.and a by-pass port connecting the same bore at a point in advance of itspiston, with the forward end of the other bore, and operating to preventloss of volume of liquid in front of the advancing piston thatappllesthe brakes.

22. In a duid-actuated brake apparatus for automobiles havingbrake-cylinders at the wheels, the combination of a master cylinderhaving a forward bore `and a rear bore, a plunger having a pistoncorresponding to each of said bores, said cylinder having a by-pass portpassing out through itswall in advance of the forwardpistonandleadingintotherearboreaheadofthe rear piston, means forsupplying operating liquid to the said bores, and a connection from theforward bore leading to the wheel brake cylinders, saldi-ear .pistonoperating to prevent emux through the by-pass from the forward cylinderas the forward piston advances.

23. In a vhydraulic brake apparatus for automobiles, the combination ofa master cylinder having a bore with a piston and a chamber back of 'thepiston, said cylinder having a port leading into the same at a pointforward of the piston when the piston isin its inactive position andleadingaround to the chamber back of the piston, said cylinder having anoutlet leading to the bra-lees at the wheels, and means for maintain-`ing pressure in the liquid in the said chamber at the back or' thepiston when the piston is moved forwardlyto apply the brakes and therebyprevent loss oi liquid through the port from the forward end of thecylinder.

24. In a duid-actuated brake apparatus for an automobile havingduid-actuated brake cylinders at the wheels, the combination of cylindermeans having two bores, pistons mounted in the said bores, means forimparting movement from one piston to the other, means connecting one ofsaid bores with the Wheel brake cylinders to apply the brakes, saidcylinders having a bypass port connecting the last named bore at a pointin advance of its piston, with the forward end of the other bore and areservoir for supplying the operating fluid to the cylinder means withmobiles, having hydraulic brake cylinders at the wheels, the combinationof a master cylinder having' a bore with a piston, connections betweenthe `bore of said master cylinder and said wheel cylinders, and achamber back of the piston independent o f the brake cyiinders at thewheels, said cylinder having a by-pass port leading into the bore at apoint forward of the piston`when the piston is in its inactive position'and leading around to the chamber back of the piston, and means forpreventing escape of liquid through the oy-pass port into therearchamber from the forward part of the cylinder when the pistonadvances. v

26. In a hydraulic brake apparatus for automobiles; a master cylinderhaving a bore with a piston therein, having a chamber back of thepiston, and having a port leading into the bore at a point forward ofthe piston when the piston is in its inactive position, said portcommunicating with the chamber back of the piston; and means formaintaining and developing pressurein the liquid in the said chamber atthe back of the piston when the piston is moved forwardly to apply thebrakes and thereby preventing loss o! liquid through the port from theforward end of the cylinder.

27. In a. hydraulic brake apparatus for automobiles; brakes; a mastercylinder provided with a piston and formed with a chamber back of thepiston and with a port leading into the cylinder at'a point forward oithe pistonv when the piston is in its inactive position, said portcommunicating with the chamber back of the piston; means connecting saidcylinder with the brakes; and means for maintaining pressure in theliquid in'said chamber at the back ot the piston when the piston ismoved forwardly to apply the brakes and thereby preventing loss ofliquid through-the port from the forward end of the cylinder.v

28. In a hydrauli wheels, a master cylinder having a bore, a pisders atthe wheels and with a bypass port leading into the bore at a pointforward of the piston when the piston is in its inactive position andconnected with the chamber back of the piston;

and means forpreventing escape of liquid through the bypass port intothe rear chamber from the forward part of the cylinder when the pistonadvances.

29. A brake system comprising a wheel brake,

a fluid motor associated therewith, fluid lines connected to said wheelmotor, and a double diameter cylinder connected to said fluid lines andcontaining a two part' piston device of corresponding diameters andarranged with a space between the v-two parts, in combination with areserve 'liquid supply conmiunioating with the space between the twoparts of the piston and having a check valve opening toward said space,means cooperating with said piston device for moving said device forapplying the brakes, and an auxiliary chamber into which movement of thepiston device pumps liquid from said space and vwhich communicates withthe cylinder ahead of the piston device.

30. In hydraulic brake apparatus for automobiles, the combination of acylinder; two piston heads positioned within the cylinder bore mountedto move in the cylinder, means connecting the same for advancement inunison; a' reservoir connected to deliver liquid at all times to theinterior of the piston lback of the forward piston head; and meanslconnected with the piston heads for advancing the same to compressliquid forward of the forward piston head and thereby apply the brakes,saidpiston heads having a position of rest and said cylinder having aport j ust in advance -of the forward piston head when in said positionof rest, said cylinder having a passage between the interior of thecylinder back of the forward piston head with the port and said cylinderhaving an outlet at its forward end for connection to the brakes; S

31. In hydraulic brake apparatus for automobiles, the combination of acylinder, two piston heads mounted to move in the cylinder;'meansconnecting the same for advancement in unison; means connected with thepiston heads for .advancing the same to compress liquid forward of theforward piston head and thereby apply the brakes, said piston headshaving a .position of rest and said cylinder having a port for-theoperating fluid just in advance of the forward piston head when in saidposition of rest, andsaidcylinder having a passage between the interiorof the cylinder back .of the forward piston head with the port, aconnection for connecting the forward end of the cylinder to the wheelbrakes, anda reservoir for the operating liquid connected with thecylinder to deliver operating liquid at all times to the interior ofi,the cylinder back of the forward piston head.

32. In hydraulic brake apparatus' for automobiles, the combination of acylinder; a plunger including twoV separated piston heads positionedywithin the cylinder bore and mounted to ,move in the cylinder; meansconnected with the plunger for advancing the same'to compress liquidforward of said piston heads and thereby to apply the brakes; saidyplunger having a position of rest and said cylinder having a port forthe operating' fluid just in advance of the forward piston head whensaid'plunger is in saidy position of rest, said cylinder having apassage between the interior of the cylinder back of the forward pistonwith the port, and said cylinder having an outlet at its forward'end forconnection to the brakes, and1 a 4supply reservoir for operating liquidconnected with the cylinder to deliver operating liquid at all times tothe interior of the cylinder back of the forward piston head.

33. Hydraulic brake apparatus comprising a fluid pressure cylinder; areservoir associated with said cylinder and positioned above saidcylinder; a piston,- having two separated heads, positioned in saidcylinder, adapted to occupy anormal rearward position therein when thebrake apparatus is released, means including said piston for preventingflow of liquid rearward of the cylinder past the forward head While attimes allowing flow of liquid forward of the cylinderpast the forwardhead, means for connecting the reservoir at all times to said cylinderat a pont'rearwmd of the normal position of the forward head; and meansfor operating said piston.

34. Hydraulic brake apparatus comprising a fluid pressure cylinderhaving a port; reservoir means associated with said cylinder andpositioned above said cylinder and communicating with said port; a cupwasher; a piston, having a forward head cooperating with said washer insaid cylinderfto prevent flow of liquid past said head rearward of thecylinder and also having a rearward head and having a recessformed-between'said heads, said piston being positioned in said cylinderto occupy a normal rearward position therein when the brake apparatus isreleased in which the forward head is positioned just rearward of saidport, said cupwasher for the forward head preventing flow of liquid pastthe forward head rearward of the cylinder; means for connecting thereservoir means to supply liquid at all'times to said recess andmanually oper`` ated means for operating said piston to cause saidforward head to move forward past said port.,

35. In hydraulic brake apparatus, a master cylinder formed with a bore,a pair of pistons positioned in said bore, mechanical means connectingsaid pistons, means for reciprocating said pistons in said bore, sealingcups secured to the front of each of said pistons and arranged toprevent passage of fluid rearwardly past said pistons, means forsupplyingfluid at all times to the space. between the pistons, means forsupplying'fluid to said cylinder forwardly of the .forward piston whensaid apparatus is in its released condition, and a passage between thespace between the pistons and said last named means.

36. A hydraulic brake system using a. brake liquid comprising a mastercylinder, a piston in said cylinder having apacking at each end thereofand formed with a recess between said packings,

a reservoir means connected to deliver liquid at all times to therecessed portion of the said piston, means for preventing movement ofliquid from the portion of the cylinder in front of the piston to the'recessed portion of the piston while allowing fluid to flow from therecessed portion to the portion of the cylinder infront of the piston,and means for conducting excess liquidfrom the forward portion of thecylinder to the reservoirv means when the piston is in its rearwardposition.

3'1.. In hydraulic brake apparatus, a ,wheel cylinder, a mastercylinder, a piston in said master cylinder dividing it into a forwardchamber and a rear chamber, a fluid connection between said forwardchamber and said wheel cylinder, a supply reservoir normally maintainedunder superatmospheric pressure,y a supply reservoir normal- 1ymaintained under atmospheric pressure, a uid connection between said rstnamed reservoir and said forward chamber, and a fluid connection betweensaid second named reservoir and said rearward chamber.

38. In a hydraulic brake system adapted to be used with a pluralityofbrakes, each provided with wheel cylinders for actuating said brakes, amaster cylinder provided with a plurality of pis- 'tons dividing saidmaster cylinder intona plurality of chambers, a uid connection betweenone of said chambers and one of said wheel cylinders, a iiuid connectionbetween/another of said chambers and another of saidwheel cylinders,separate supply compartments, each separately connected to one of saidmaster cylinder chambers, and' mechanical connections between saidpistons for causing them to move in unison.

39. In fluid pressure apparatus, a plurality of brakes. a mastercylinder, mean's dividing said master cylinder into a plurality ofchambers, a

"connection extending between one of said chambers and one of saidbrakes, a connection extending between another said chamberand anotherof said brakes, a pair of pistons positioned on said master cylinder forforcing uid from-said chambers to said brakes respectively, and a lostmotionconnection between said pistons for normally insuring equalizationof pressure between said -brakes and at the same time minimizing thechance of'falure of all of said brakes upon the failure of one.

40. In a hydraulic brake system, a master cylinder, a wheel cylinder,conduit means interconnecting said cylinders, a reservoir, a piston inSaid master cylinder, a iiuid connection from ythe reservoir to themaster cylinder at a point in advance of the normal' position of thepiston therein, a second fluid connection from the reservoir to themaster cylinder at a point behind the normal position of the pistontherein, said reservoir being elevated to produce a slight pressure insaid conduit means and cylinders, a rod 20 for operating said piston, asealing cup secured to said piston, and a sealing means for said lastnamed iiudconnection.

EUGENE G. CARROLL. '25

